1. Field of the Invention
The present invention relates to catalytic cracking apparatus of petroleum hydrocarbons in the absence of hydrogen and, more particularly, to a catalytic cracking reaction-regeneration system for the application in laboratories.
2. Description of Background and Related Art
Catalytic cracking is an important refining process for producing motor fuel oils and chemical feedstocks and is an effective means for lightening heavy oils. Therefore, catalytic cracking process has been a researching point of studies in the refinery industry for decades. As known to all, the development of a novel process and catalyst must under go a rather long investigation course from bench-scale exploration, via pilot plant, to industrial application. Therefore, whether the data in laboratories are prospective, in other words, whether said data are able to reflect the anticipated results of the industrial application is a key to the success of the technical development. There are two ways for researching catalytic cracking processes in laboratories: one is to use a fixed fluidized-bed unit, and the other is to use a continuous reaction-regeneration fluidized-bed unit or a riser unit. The fixed fluidized-bed unit is small in scale, convenient, flexible, cheap, and with the use of a small amount of oil and catalyst; so, it is widely adopted by many research institutes and refineries mainly for evaluating catalysts. Small or medium units for continuous reaction-regeneration unit can better simulate the conditions in an industry-scale unit and match the industrial data in the yield and the quality of the resultant products.
There are not many reference documents in the prior art concerning laboratory catalytic cracking units. The relevant information can be referred to U.S. Pat. No. 6,069,012 and the circulating riser catalytic cracking experimental unit of GRACE DAVISON CORPORATION. However, the function of these units is rather simple and cannot meet the needs of the evaluation of various novel catalysts and the development of the processing.
U.S. Pat. No. 6,069,012 discloses an improved fixed fluidized-bed reactor. The improvement in the structure of this reactor is embodied in the following two aspects: (1) adoption of a height-variable feeding sleeving, the inner tube of which is used to deliver oil feedstocks, while the jacket is used to deliver the fluidizing gas; and (2) a fluidizing gas nozzle is additionally equipped at the center of the bottom of the reactor. The above improvements in the structure enable the fixed fluidized-bed reactor to adjust the reaction time by modifying the height of the feeding nozzle. Besides, the addition of the fluidizing gas nozzle at the bottom of the reactor can improve the fluidized state of the catalyst; however when the linear speed of the reactor bed is equal to or greater than 18.2 cm/sec, a violent turbulent flow and slugging may happen to the catalyst bed, the catalyst may be elevated to the top of the reactor and deviated from the isothermal section of the reactor, which leads to ineffective control of the reaction temperature. Because of the limitation of the above bed linear speed, such a reactor can only be experimented under ordinary catalytic cracking reaction conditions, but is not suitable for the special reaction requirements of the present catalytic cracking field for carrying out reaction under high temperature, high catalyst/oil ratios, high gas outputs, and so on.
One of the most important process parameters of fluidized catalytic cracking is the contact time of hydrocarbons and the catalyst. Recent studies show that 90% of the feedstock conversion takes place during a very short time of the feedstock contacting with the catalyst. Based on this knowledge, the structure of existing units is gradually reformed to raise the yield and quality of the product. However, a shorter feedstock-oil contact time needs the match of a higher catalyst/oil ratio to achieve a desirable conversion depth of hydrocarbons and oil. Therefore, either the design of a new unit, or the reformation of an old unit should meet the requirement in this respect.
In a continuous reaction-regeneration system, the shortening of the reaction time can be realized by using a down-flow reactor or instantaneous reaction structure with ultrashort time. In addition to a short oil/catalyst contact time, down-flow reactor can greatly reduce backmixing and thereby reduce the secondary reactions which are unfavorable to the product distribution. The instantaneous reaction structure can examine the positive influence of the ultrashort reaction time on the distribution and quality of the product.
As for the present continuous reaction-regeneration experimental units for catalytic cracking both at home and abroad, no reports have been found relating to the integration of riser, down-flow operation, and instantaneous reaction structure which results in flexible switch their-between.